2-Chloroquinoline-3-carboxylic acid

The crystal structure of the title compound, C10H6ClNO2, can be described by two types of crossed layers which are parallel to (110) and (10). The crystal packing is stabilized by intermolecular C—H⋯O and O—H⋯N hydrogen bonds, resulting in the formation of a two-dimensional network and reinforcing the cohesion of the structure.

The crystal structure of the title compound, C 10 H 6 ClNO 2 , can be described by two types of crossed layers which are parallel to (110) and (110). The crystal packing is stabilized by intermolecular C-HÁ Á ÁO and O-HÁ Á ÁN hydrogen bonds, resulting in the formation of a two-dimensional network and reinforcing the cohesion of the structure.
We are grateful to all personnel of the laboratory PHYSYNOR, Université Mentouri-Constantine, Algé rie for their assistance. Thanks are due to MESRS (Ministé re de l'Enseignement Supé rieur et de la Recherche Scientifique -Algé rie) for financial support.

Comment
In a continuation of our previous work related to the preparation of α-aminonitrile (Ladraa et al., 2009;Belfaitah et al., 2006) and in order to prepare chiral N-deprotected α-aminonitrile, we have explored the oxidative debenzylation of N-protected α-aminonitrile. The removal of the chiral auxiliaries has already been investigated using ceric ammonium nitrate (CAN) (Bhanu Prasad et al., 2004). Surprisingly, our attempts to remove the chiral auxiliary using CAN were failed to undergo the desired adduct and led to the 2-chloroquinoline-3-carboxylic acid (I). This unexpected cleavage of 2-[(S)-2-chloro-3quinolyl]-2-[(R)-1-(4-methoxyphenyl) ethylamino]acetonitrile may result from the decomposition of the α-aminonitrile into cyanide and imine which in turn undergo hydrolysis/oxidative sequence. In this paper, we report the structure determination of compound (I), resulting from unwanted decomposition of chiral N-protected α-aminonitrile.
The molecular geometry and the atom-numbering scheme of (I) are shown in Fig. 1. The two rings of quinolyl moiety are fused in an axial fashion and form a dihedral angle of 0.42 (9)°. The crystal packing can be described by two types of crossed layers which quinolyl ring is parallel to (110) and (-110) planes respectively (Fig. 2). The crystal packing is stabilized by inter and intramolecular hydrogen bonds (O-H···N and C-H···O) linked molecules in the same layer, resulting in the formation of a two dimensional network and reinforcing a cohesion of structure. Hydrogen-bonding parameters are listed in table 1.

Experimental
A solution of 327 mg (3 eq., 0.59 mmol.) of ceric ammonium nitrate (CAN) in 1 ml of water was added to precooled stirred solution of 2-[(S)-2-chloro-3-quinolyl]-2-[(R)-1-(4-methoxyphenyl) ethylamino] acetonitrile (70 mg, 0.19 mmol) in 9 ml of CH 3 CN. After completion of the reaction (checked by TLC), the reaction mixture was poured into cold water and the residue obtained was filtered off. Crystals of (I) suitable for X-ray analysis were obtained by slow evaporation of the filtrate.

Refinement
All non-H atoms were refined with anisotropic atomic displacement parameters. All H atoms were localized on Fourier maps but introduced in calculated positions and treated as riding on their parent C and O atoms. (with C-H = 0.95Å -O-H =0.84Å and U iso (H) =1.2 or 1.5(carrier atom)). Fig. 1. (Farrugia, 1997) the structure of the title compound with the atomic labeling scheme. Displacements are drawn at the 50% probability level.

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.
Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq C1 0.1466 (